112 N. J. Mosquito Extermination Association 



delay and the consequent escape of several broods of mosquitoes 

 but it has this compensating advantage that when the work is fin- 

 ished, you know the area in question is as nearly mosquito proof as 

 man's ingenuity and the application of good engineering practice can 

 make it. It is far better to drain one area completely than to attempt 

 to drain many areas partially and when a drainage system is de- 

 signed simply to meet conditions which are apparent at the time the 

 drainage is needed, the system cannot be expected to prove service- 

 able under circumstances that might have been but were not taken 

 into consideration. 



The type of drainage therefore that is best adapted for salt marsh 

 drainage cannot be empirically set down but must be largely gov- 

 erned by local conditions as determined by intelligent study. If 

 open ditching is decided on, the system should be laid out so that 

 no point in any lateral ditch will be more than 2,000 feet from an 

 outlet. Otherwise in long ditches there may be a section of the 

 ditch in which the water does not change with the tides and there 

 is always the danger that breeding may take place in such ditch sec- 

 tions. Well constructed and scientifically designed open ditching 

 systems are the cheapest now in use. They have the advantage of a 

 free circulation and the change of water with each flowing and ebb- 

 ing tide. They have the further advantage of allowing ready access 

 to fishand thus providing a supplemental auxiliary patrol to prevent 

 any ditch breeding. Where circumstances warrant its use, the open 

 system of ditching is to be recommended. 



However, on some areas, this system of drainage is not practical 

 sometimes because the sections are sunken to such a level that the 

 tide-pull is insufficient to allow rapid or complete drainage, some- 

 times because the place to be drained is so cut off that the outlets 

 are not large enough to drain off both tide water and storm water in 

 the required time and sometimes because there is a substrata of 

 clay under the meadow which forms a natural basin and prevents 

 good seepage so that water which overflows on the high tide is not 

 drawn back into the ditch on the receding tide, but remains on the 

 meadow surface to become stagnant and to breed. Under such con- 

 ditions, open ditching will not avail and the drainage system must 

 be varied to meet the facts as found. If a ditching system will not 

 handle both tide-water and storm quickly enough to do away with 

 mosquito breeding, the plan usually followed is to exclude the tide 

 water altogether by means of dikes and tide-gates and make the 

 ditches of sufficient capacity to handle the storm water and surface 



